Yellow phosphorus furnace electrode paste and preparation method thereof

Abstract

The invention discloses a yellow phosphorus furnace electrode paste and a preparation method thereof, and belongs to the technical field of yellow phosphorus furnace production, the yellow phosphorus furnace electrode paste comprises the following raw materials by mass: 55-65% of anthracite particles, 20-25% of petroleum coke, 5-10% of graphite chips, 18-25% of a composite binder, 0.3-1.5% of a composite antioxidant and 1.5-4.5% of an additive; the yellow phosphorus furnace electrode paste provided by the invention is produced according to the preparation method provided by the invention, and the resistivity, compressive strength and oxidation resistance can be synchronously improved through the design of carbon material multistage particle size distribution, a nano-reinforced composite binder and a synergistic anti-oxidation system in combination with an efficient drying and densification process; the problem that an existing electrode paste is poor in density and performance is effectively solved.

Description

Technical Field

[0001] The invention relates to the field of yellow phosphorus electric furnace production, in particular to a yellow phosphorus furnace electrode paste and a preparation method thereof. Background Art

[0002] Yellow phosphorus furnace electrode paste is a key conductive material used in yellow phosphorus electric furnace production, primarily for the preparation of self-baking electrodes. The electric furnace method is the primary process in yellow phosphorus production. The electrode paste gradually sinters and carbonizes at high temperatures (1200-1500°C) to form a conductive electrode body. This paste plays a key role in transmitting current and generating a high-temperature arc to decompose phosphate rock (apatite).

[0003] Traditional electrode paste is usually prepared based on anthracite and petroleum coke as aggregates and coal tar as a binder. However, the preparation process is subject to a series of problems and challenges. First, in the traditional method, a hot air drying process is used, which usually takes 2-4 hours. This is not only time-consuming but also difficult to stably control the moisture content of the raw materials, thereby affecting the mixing uniformity of the electrode paste. The electrode paste prepared in this way has a high resistivity and low compressive strength, resulting in unstable arc and the electrode is prone to breakage at high temperatures. Secondly, the electrode surface is easily oxidized in a high temperature environment, resulting in a loss rate of up to 1.5-2.0 kg / ton of phosphorus, which undoubtedly increases production costs. Furthermore, the use of coal tar as a single binder is prone to cracks after high-temperature carbonization, further reducing the structural density of the electrode, thereby affecting its overall performance. The ash content of conventional electrode paste is generally higher than 10%, which leads to a decrease in conductivity, and local overheating is prone to occur in the high-temperature arc zone, increasing the risk of electrode breakage.

[0004] In recent years, the industry has attempted to improve the formulation and technology of electrode paste. For example, some patents use a compound of calcined petroleum coke and graphite chips to reduce the ash content to 8 to 10%, but fail to solve the problem of insufficient rheological properties of the binder at high temperatures. Other patents propose to improve the oxidation resistance by adding micron-sized silicon carbide, but the particle size distribution is unreasonable, resulting in a decrease in the density of the material. Although these improvements have improved the performance of the electrode paste to a certain extent, its preparation process mostly uses conventional hot air drying and atmospheric pressure kneading, which is not only time-consuming but also easily leads to oxidation of the carbon material and uneven distribution of the binder, reducing the volume density of the finished product. Therefore, developing a new type of electrode paste that improves the high-temperature strength, conductive stability and corrosion resistance of the electrode by optimizing the grading of the carbon material, introducing a nano-enhanced bonding system and a composite antioxidant component, and matching it with an efficient preparation process has become a technical problem that urgently needs to be solved. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned background technical difficulties and provide a yellow phosphorus furnace electrode paste and a preparation method thereof that can achieve simultaneous improvement in resistivity, compressive strength and oxidation resistance.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a yellow phosphorus furnace electrode paste, the raw material composition of which includes, by mass percentage, 55-65% anthracite particles, 20-25% petroleum coke, 5-10% graphite chips, 18-25% composite binder, 0.3-1.5% composite antioxidant and 1.5-4.5% additives.

[0007] Furthermore, the anthracite particles are crushed into particles by using coal blocks with fixed carbon ≥85% and ash ≤8%, wherein the particle size distribution of the anthracite particles is as follows: coarse particles of 3-5 mm account for 40-50%, medium particles of 1-3 mm account for 30-40%, and fine powder of ≤0.5 mm accounts for 10-20%.

[0008] Furthermore, the composite binder accounts for 18-25% of the total mass of the electrode paste, and is composed of 70-80% coal tar pitch, 15-25% modified phenolic resin and 2-5% nano-silicon carbide, wherein the particle size of the nano-silicon carbide is 50-100nm.

[0009] Furthermore, the modified phenolic resin is furfural-modified phenolic resin with a softening point of 90-110°C.

[0010] Furthermore, the composite antioxidant consists of 0.2-1.0% boron carbide and 0.1-0.8% silicon nitride.

[0011] Furthermore, the additive consists of 1-3% metallic silicon powder and 0.5-1.5% titanium boride.

[0012] Furthermore, the method for preparing the yellow phosphorus furnace electrode paste comprises the following steps: (1) Raw material pretreatment: Mix anthracite particles, petroleum coke and graphite chips in a mass ratio of 55-65:20-25:5-15 and crush them into particles with a size of ≤5 mm; (2) Microwave vacuum drying: drying the mixed carbon material obtained in step (1) at a microwave power of 5 to 10 kW and a vacuum degree of -0.08 to -0.1 MPa for 20 to 40 minutes, controlling the moisture content to ≤0.5%; (3) Preparation of composite binder: Coal tar pitch and modified phenolic resin are mixed in a mass ratio of 7-9:1-3, heated to 160-180°C to melt, nano-silicon carbide powder with a particle size of 50-100 nm is added, and stirred to form a composite binder; (4) Kneading: preheating the carbon material dried in step (2) to 120-150°C, and kneading it with the composite binder prepared in step (3) in a biaxial kneader at a mass ratio of 70-80:20-30 for 30-50 minutes, maintaining the kneading temperature at 140-160°C, to prepare a paste; (5) Molding: The paste obtained in step (4) is hydraulically extruded into a cylinder with a diameter of 150 to 300 mm, and then vacuum-packed after cooling.

[0013] Furthermore, the pressure of the hydraulic extrusion molding in step (5) is 15 to 25 MPa, and the extrusion rate is 2 to 5 cm / min.

[0014] The present invention provides a yellow phosphorus furnace electrode paste and a preparation method thereof, which have the following beneficial effects: The yellow phosphorus furnace electrode paste formula provided by the present invention is produced according to the preparation method of the present application. It can achieve simultaneous improvement of resistivity, compressive strength and oxidation resistance through the design of multi-level particle size distribution of carbon materials, nano-reinforced composite binder and synergistic antioxidant system, combined with efficient drying and densification processes; and effectively solves the problems of poor density and performance of existing electrode pastes. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of the production process of the present invention. DETAILED DESCRIPTION

[0016] The technical solutions of the present invention are described clearly and completely below in conjunction with specific embodiments of the present invention. The described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0017] Example 1 The present invention provides a yellow phosphorus furnace electrode paste, the raw material composition of which includes, by mass percentage, 55-65% anthracite particles, 20-25% petroleum coke, 5-10% graphite chips, 18-25% composite binder, 0.3-1.5% composite antioxidant and 1.5-4.5% additives. The present application provides a yellow phosphorus furnace electrode paste, the raw material composition of which includes, by mass percentage, 60% anthracite particles, 22% petroleum coke, 8% graphite chips, 20% composite binder, 0.8% composite antioxidant and 3.2% additives.

[0018] The anthracite particles described in this application are made of coal blocks with fixed carbon ≥85% and ash ≤8% and crushed into particles, wherein the particle size distribution of the anthracite particles is as follows: coarse particles of 3 to 5 mm account for 40 to 50% as skeleton support, reducing large pores to ensure the continuity of the current transmission path, medium particles of 1 to 3 mm account for 30 to 40% to fill the gaps between coarse particles, reducing the porosity below 8%, and fine powder ≤0.5 mm accounts for 10 to 20% to further compact the micropores and reduce the interface resistance; further, the anthracite particles of this application Coal blocks with 86% fixed carbon and 7% ash are crushed into particles, of which the particle size distribution of anthracite particles is as follows: coarse particles of 3-5 mm account for 45%, medium particles of 1-3 mm account for 35%, and fine powder of ≤0.5 mm accounts for 20%. This application can make the particle size porosity reach 8% (the traditional single particle size porosity is 12%) and the volume density reach 1.8g / cm³ (the traditional 1.6g / cm³) through multi-level carbon material filling, so that it can build a dense conductive skeleton and improve its compressive strength.

[0019] The composite binder accounts for 18-25% of the total mass of the electrode paste, and is composed of 70-80% coal tar pitch, 15-25% modified phenolic resin and 2-5% nano-silicon carbide, according to the total mass percentage of the composite binder, wherein the particle size of the nano-silicon carbide is 50-100nm. The composite binder of the present application is preferably composed of 75% coal tar pitch to provide basic adhesion, a softening point of 80-120°C to ensure mixing fluidity, 20% modified phenolic resin, and a residual carbon rate of ≥65% (the residual carbon rate test standard refers to GB / T1429 -2015), which forms a glassy carbon reinforcement phase after carbonization and constructs a nano-conductive path composition by dispersing 5% nano-silicon carbide in a binder; the present application forms a "point-line-surface" conductive network through nano-silicon carbide, and the resistivity is reduced to 50-55μΩ·m, which is significantly improved compared to the traditional resistivity of 70μΩ·m; and the modified phenolic resin is combined with nano-silicon carbide and used with reference to the preparation method of the present application, which can enhance the thermal conductivity and anti-stripping properties of the binder after carbonization, thereby enhancing the density of the conductive network after carbonization.

[0020] The modified phenolic resin is a furfural-modified phenolic resin with a softening point of 90-110°C. The modified phenolic resin of the present application is composed of phenol, formaldehyde and furfural. Phenol and formaldehyde are initially polycondensed under NaOH to generate a linear phenolic resin. Furfural is added to replace 20-30% of the formaldehyde, and further cross-linked under acidic conditions to form a furan ring-phenol copolymer network. The final product is a dark brown viscous liquid with a softening point of 90-110°C and a residual carbon rate of ≥65% (the residual carbon rate of traditional phenolic resin is <50%).

[0021] The composite antioxidant is composed of 0.2-1.0% boron carbide and 0.1-0.8% silicon nitride. The composite antioxidant of the present application is preferably composed of 0.5% boron carbide and 0.3% silicon nitride. The boron carbide of the present application generates a B2O3 glass layer (melting point 450°C) at high temperature, covering the electrode surface; silicon nitride is oxidized to generate SiO2 and Si2N2O, filling the microcracks of the B2O3 layer; experiments have shown that the double-layer protection of boron carbide and silicon nitride in the present application reduces the oxidation rate by 53%. The oxide layer thickness test refers to GB / T13221-2009. After continuous operation at 1500°C for 100 hours, the oxide layer thickness is <50μm, while the traditional oxide layer thickness is >150μm. The present application can inhibit high-temperature oxidation through the synergistic effect of boron carbide and silicon nitride.

[0022] The additive is composed of 1-3% metal silicon powder and 0.5-1.5% titanium boride. The additive of the present application is preferably composed of 2% metal silicon powder with a particle size of ≤50μm and 1.2% titanium boride with a particle size of ≤10μm, which improves the mechanical strength of the electrode and reduces the resistivity.

[0023] The preparation method of the above yellow phosphorus furnace electrode paste is as follows: Figure 1 The method comprises the following steps: (1) Raw material pretreatment: anthracite particles, petroleum coke and graphite chips are mixed in a mass ratio of 55-65:20-25:5-15, and crushed into particles with a particle size of ≤5 mm. In this application, anthracite particles, petroleum coke and graphite chips are preferably mixed in a mass ratio of 60:22:8, and crushed into particles with a jaw crusher to a particle size of ≤5 mm.

[0024] (2) Microwave vacuum drying: drying the mixed carbon material obtained in step (1) at a microwave power of 5 to 10 kW and a vacuum degree of -0.08 to -0.1 MPa for 20 to 40 min, controlling the water content to ≤0.5%, achieving rapid dehydration and avoiding oxidation. Preferably, drying the mixed carbon material obtained in step (1) at a microwave power of 8 kW and a vacuum degree of -0.09 MPa for 30 min, controlling the water content to ≤0.4%, achieving rapid dehydration and avoiding oxidation.

[0025] (3) Preparation of composite binder: Coal tar pitch and modified phenolic resin are mixed in a mass ratio of 7-9:1-3, heated to 160-180°C to melt, nano-silicon carbide powder with a particle size of 50-100 nm is added to improve thermal conductivity, and stirred to form a composite binder. Preferably, coal tar pitch and modified phenolic resin are mixed in a mass ratio of 7:3, heated to 170°C to melt, nano-silicon carbide powder with a particle size of 50-100 nm is added to improve thermal conductivity, and stirred for 30 minutes to obtain a composite binder.

[0026] (4) Kneading: preheating the carbon material dried in step (2) to 120-150°C, kneading it with the composite binder prepared in step (3) in a biaxial kneader at a mass ratio of 70-80:20-30 for 30-50 minutes, maintaining the kneading temperature at 140-160°C, ensuring the paste is homogenized, and obtaining a paste; preferably, preheating the carbon material dried in step (2) to 130°C, kneading it with the composite binder prepared in step (3) in a biaxial kneader at a mass ratio of 75:25 for 40 minutes, maintaining the kneading temperature at 150°C, ensuring the paste is homogenized, and obtaining a paste; (5) Molding: The paste obtained in step (4) is hydraulically extruded into a cylinder with a diameter of 150 to 300 mm. The pressure of the hydraulic extrusion molding is 15 to 25 MPa and the extrusion rate is 2 to 5 cm / min. After cooling, the paste is vacuum packaged. Preferably, the paste is extruded into a cylinder with a diameter of 200 mm by a hydraulic press at a pressure of 20 MPa and an extrusion rate of 3 cm / min.

[0027] The applicant conducted performance tests on resistivity, compressive strength, oxidation loss rate, and drying energy consumption. The resistivity test referred to GB / T24525-2009, and the test result was 52μΩ·m; the compressive strength test referred to GB / T1431-2009, and the test result was 28MPa; the oxidation loss rate was tested at a constant temperature of 1550°C for 4 hours, and the test result was 0.75kg / ton of phosphorus; and the power consumption measurement test showed that its drying energy was 0.8kWh / kg, which is more than 12% lower than the energy consumption of traditional drying processes.

[0028] In summary, this application achieves a simultaneous improvement in resistivity, compressive strength and oxidation resistance through the design of multi-level particle size distribution of carbon materials, nano-reinforced composite binders and synergistic antioxidant systems, combined with efficient drying and densification processes.

[0029] Example 2 Based on Example 1, the applicant verified the effect of the ratio of boron carbide to silicon nitride on oxidation resistance; The total amount of composite antioxidant is fixed at 0.8%, and verification tests are carried out on the adjusted boron carbide: silicon nitride ratio of 3:1, 2:1, and 1:1. The test results are as follows: when the boron carbide: silicon nitride ratio is 3:1, the oxidation loss rate is 0.68 (kg / ton phosphorus), and B4C is dominant in forming a dense oxide layer; when the boron carbide: silicon nitride ratio is 2:1, the oxidation loss rate is 0.75 (kg / ton phosphorus), which can provide balanced protection, but is suitable for conventional working conditions; when the boron carbide: silicon nitride ratio is 1:1, the oxidation loss rate is 0.92 (kg / ton phosphorus), and excessive silicon nitride leads to an uneven protective layer.

[0030] Example 3 Based on Example 1, the applicant verified the effect of nano-silicon carbide on resistivity; the amount of nano-silicon carbide added was fixed at 4% of the binder, and all tests were carried out according to the preparation process of Example 1, only the particle size of nano-silicon carbide was adjusted, and the particle sizes of 30nm, 50-100nm, and 120nm were verified respectively. The verification results are as follows: when the particle size is 30nm, the detection shows that its resistivity is 48μΩ·m, when the particle size is 50-100nm, the detection shows that its resistivity is 49-58μΩ·m, and when the particle size is 120nm, the detection shows that its resistivity is 65μΩ·m; after verification and comparison, it was found that too small a particle size is easy to agglomerate, and actual production dispersion is difficult and the cost is high. The particle size is too large and exceeds the range, resulting in discontinuity of the local conductive network, and the performance is lower than the traditional formula; the preferred nano-silicon carbide particle size of this application is 80nm, the resistivity is 52μΩ·m, the dispersion is uniform and the cost is controllable.

[0031] Experimental Group 1 The difference between Experimental Group 1 and Example 1 is that ordinary phenolic resin is used instead of the furfural-modified resin in this application, and the other components remain unchanged. The test results are as follows: in Experimental Group 1, the residual carbon rate is 48%, the compressive strength is 16 MPa, and the resistivity is 65 μΩ·m; the residual carbon rate of this application is 68%, the compressive strength is 28 MPa, and the resistivity is 52 μΩ·m. It can be seen that the carbon skeleton of the phenolic resin provided in Experimental Group 1 is insufficient in density and the strength is reduced.

[0032] Experimental Group 2 The difference between Experimental Group 2 and Example 1 is that epoxy resin (E-51 type) is used to replace the furfural-modified resin of this application, and the other components remain unchanged. The test results are as follows: Experimental Group 2 has a residual carbon rate of 30% and poor high-temperature adhesion (easy to pulverize after carbonization). The residual carbon rate of this application is 68%, and the high-temperature adhesion is significantly better than that of Experimental Group 2. It can be seen that the carbonization residual carbon rate of the epoxy resin in the experimental group 2 is low and a continuous conductive network cannot be formed.

[0033] Experimental Group 3 The difference between Experimental Group Three and Example One is that an equal amount of silicon carbide is used instead of boron carbide in the composite antioxidant, that is, the composite antioxidant consists of 0.5% silicon carbide and 0.3% silicon nitride; through experimental comparison, it is concluded that the oxidation loss rate of the experimental group is 1.25 kg / ton phosphorus, and the compressive strength is 24 MPa, while the oxidation loss rate of the present application is 0.75 kg / ton phosphorus, and the compressive strength is 28 MPa; it can be seen that the SiC added in Experimental Group Three cannot form a continuous B2O3 protective layer during the preparation process, and the reinforcement effect of the SiC added in Experimental Group Three is significantly weaker than that of the B4C+Si3N4 combination of the present application.

[0034] Experimental group 4 The difference between Experimental Group 4 and Example 1 is that an equal amount of tungsten carbide is used to replace titanium boride. After experimental comparison, it is found that the resistivity of Experimental Group 4 is 60μΩ·m and the compressive strength is 22MPa; the resistivity of the present application is 52μΩ·m and the compressive strength is 28MPa. It can be seen that the conductivity of WC is weaker than that of TiB2, and the dispersion effect of WC is poor. The conductivity and strengthening effects of titanium boride added to the formula of the present application are component-specific.

[0035] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no nano-silicon carbide is added to the composite binder, that is, the composite binder accounts for 20% of the total mass of the electrode paste, and is composed of 15% coal tar pitch and 5% modified phenolic resin according to the total mass percentage of the composite binder; experimental comparison shows that the resistivity of Comparative Example 2 is 68μΩ·m and the compressive strength is 18MPa; the resistivity of this application is 52μΩ·m and the compressive strength is 28MPa; it can be seen that the nano-silicon carbide added to the original formula affects the performance of the conductive network reinforcement, and its performance is significantly better than that of the composite binder in Comparative Example 1 without adding nano-silicon carbide.

[0036] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the composite binder uses only 20% coal tar pitch; experimental comparison shows that the resistivity of Comparative Example 2 is 65μΩ·m, the compressive strength is 16MPa, and the carbonization residual carbon rate of the binder is 48%; the resistivity of the present application is 52μΩ·m, the compressive strength is 28MPa, and the carbonization residual carbon rate of the binder is 68%. It can be seen that the modified phenolic resin added to the formula of the present application affects the stability of the carbonization structure, and the performance of its composite binder is significantly better than that of the composite binder in Comparative Example 2 using only 20% coal tar pitch.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0038] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A yellow phosphorus furnace electrode paste, characterized in that: The raw material composition includes, by mass percentage, 55-65% of anthracite particles, 20-25% of petroleum coke, 5-10% of graphite chips, 18-25% of composite binder, 0.3-1.5% of composite antioxidant and 1.5-4.5% of additives.

2. The yellow phosphorus furnace electrode paste according to claim 1, characterized in that: The anthracite particles are crushed into particles using coal blocks with fixed carbon ≥85% and ash ≤8%, wherein the particle size distribution of the anthracite particles is as follows: coarse particles of 3-5 mm account for 40-50%, medium particles of 1-3 mm account for 30-40%, and fine powder of ≤0.5 mm accounts for 10-20%.

3. The yellow phosphorus furnace electrode paste according to claim 1, characterized in that: The composite binder accounts for 18-25% of the total mass of the electrode paste and is composed of 70-80% coal tar pitch, 15-25% modified phenolic resin and 2-5% nano-silicon carbide, wherein the particle size of the nano-silicon carbide is 50-100nm.

4. The yellow phosphorus furnace electrode paste according to claim 3, characterized in that: The modified phenolic resin is furfural-modified phenolic resin with a softening point of 90-110°C.

5. The yellow phosphorus furnace electrode paste according to claim 1, characterized in that: The composite antioxidant consists of 0.2-1.0% boron carbide and 0.1-0.8% silicon nitride.

6. The yellow phosphorus furnace electrode paste according to claim 1, characterized in that: The additive consists of 1-3% of metallic silicon powder and 0.5-1.5% of titanium boride.

7. The method for preparing yellow phosphorus furnace electrode paste according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Raw material pretreatment: Mix anthracite particles, petroleum coke and graphite chips in a mass ratio of 55-65:20-25:5-15 and crush them into particles with a size of ≤5 mm; (2) Microwave vacuum drying: drying the mixed carbon material obtained in step (1) at a microwave power of 5 to 10 kW and a vacuum degree of -0.08 to -0.1 MPa for 20 to 40 minutes, controlling the moisture content to ≤0.5%; (3) Preparation of composite binder: Coal tar pitch and modified phenolic resin are mixed in a mass ratio of 7-9:1-3, heated to 160-180°C to melt, nano-silicon carbide powder with a particle size of 50-100 nm is added, and stirred to form a composite binder; (4) Kneading: preheating the carbon material dried in step (2) to 120-150°C, and kneading it with the composite binder prepared in step (3) in a biaxial kneader at a mass ratio of 70-80:20-30 for 30-50 minutes, maintaining the kneading temperature at 140-160°C, to prepare a paste; (5) Molding: The paste obtained in step (4) is hydraulically extruded into a cylinder with a diameter of 150 to 300 mm, and then vacuum-packed after cooling.

8. The method for preparing yellow phosphorus furnace electrode paste according to claim 7, wherein: The pressure of the hydraulic extrusion molding in step (5) is 15 to 25 MPa, and the extrusion rate is 2 to 5 cm / min.

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